The goal of this application is to establish the independent research career of the candidate in the study of chronic lung disease, including that affecting individuals with cystic fibrosis (CF). The candidate is a pediatric pulmonary fellow with the career goal of developing an active program of disease-related basic research as a faculty member at a medical school. The training environments are the laboratory of the sponsor, Dr. Samuel Miller, at the University of Washington School of Medicine, and the CF Center at Children's Hospital and Regional Medical Center in Seattle, directed by the co-sponsor, Dr. Ronald Gibson. The proposed project seeks to clarify molecular mechanisms underlying chronic lung infection and inflammation in individuals with CF. The opportunistic pathogen Pseudomonas aeruginosa (PA) infects the lungs of most individuals with CF, frequently (but not invariably) causing severe progressive lung injury and premature death. Study of the interaction between PA and the CF lung is necessary to understand both the cellular processes that promote or permit CF lung infection, and the precise means by which PA interacts with lung cells to cause airway damage. The structure of lipopolysaccharide (LPS), the principal constituent of Gram-negative bacterial surfaces, appears to play a pivotal role in both microbial and human aspects of this interaction. The candidate's preliminary results indicate that resistance of laboratory and clinical isolates of PA to antimicrobial peptides (key components of host innate immunity) correlates with alterations in the structure of the lipid A moiety of LPS. Moreover, mutation of a PA locus that regulates LPS-modifying enzymes influences the antimicrobial peptide resistance phenotype. The microbiological phase of the project thus seeks to define PA genes necessary for this putative resistance mechanism, and to identify potential inhibitors using antimicrobial peptide-resistant strains. The human phase of the project builds on the clinical observation that some individuals with a severe CF genotype and chronic PA airway infection nevertheless have minimal lung disease. A case-control design will be utilized to test the hypothesis that polymorphisms in innate immune genes may limit CF lung disease. Those innate immune genes encoding the LPS receptor are leading candidates as CF modifier loci, based on the recent finding that CF-specific PA LPS structures have increased inflammatory activity. When prevalence of an LPS receptor variant differs in mild and severe CF lung disease, receptor function will be assayed in cell culture models of LPS signaling. Identifying innate immune genes as modifiers of the CF lung phenotype may suggest new avenues for treating the inflammatory consequences of CF airway infection.